Calcium supplements and heart attacks 'linked'

Calcium pills “do more harm than good' the Daily Mail has reported. By contrast, the Telegraph tells us there is “no need to panic over new calcium heart attack research”. So, which to believe?

These headlines are based on the findings of a large German study that looked at the association between calcium intake and incidents of heart attack, strokes and deaths from cardiovascular disease over a period of 11 years.

Calcium supplements are often given to elderly people and women who have gone through the menopause, in an effort to keep their bones healthy.

Researchers found no link between the amount of calcium in people’s diet and their risk of stroke or cardiovascular deaths. However, people using calcium supplements as their only form of supplement had more than twice the risk of heart attack compared with people who didn’t take any vitamin supplements.

This suggests that there may be an increased risk of heart attack due to calcium supplements, but on its own doesn’t mean that these supplements cause heart attacks as other factors may be at play. The researchers believed that people who take supplements may be generally less healthy than those who don’t (assuming they take supplements for a health reason) so they tried to adjust for other risk factors such as smoking habits and exercise levels. However, it is unlikely they adjusted for all the influencing factors and so we still cannot be certain that calcium supplements increase heart attacks.

Previous research based on stronger study designs has also supported a link between calcium supplements and heart disease. If you are considering taking calcium supplements, you need to base your decision on your own circumstances, balancing the benefits with the potential risks.

Do not be alarmed by the media headlines. If you have been prescribed calcium supplements do not stop taking your medication. Speak to your doctor if you have particular concerns.

Where did the story come from?

The study was carried out by researchers from universities in Germany and Switzerland and was funded by a grant from Deutsche Krebshilfe (German Cancer Aid).

This study drew widespread coverage that focused on the risks reported for calcium supplementation. The Daily Mail took this too far, suggesting that “calcium pills taken by hundreds of thousands of women ‘could double risk of heart attack and do more harm than good'”, a claim not backed up by the study. Encouragingly, the majority of the articles included a balanced view of the research and reassured readers neither to worry unduly nor to stop their medication without consulting their GP. The “no need to panic” headline from the Daily Telegraph’s website was refreshing as it contradicted sensationalist articles among other tabloids and was the most sensible message reported. Unfortunately, its printed edition’s front-page headline (“Calcium pills ‘can double the risk of heart attack’”) struck a much more alarmist tone.

What kind of research was this?

This was an analysis of data already collected from a large German cohort study.

Calcium supplements are often given to elderly people and women who have gone through the menopause in an effort to keep their bones healthy and prevent osteoporosis. The authors reported that dietary calcium intake (calcium consumed naturally through food) has been linked to a lower risk of heart-related disease in previous research. However, they stated that no strong evidence supports the claim that taking additional calcium supplements is beneficial to heart health and they highlighted some studies suggesting that supplementation may increase the risk of heart attack.

This study aimed to examine the association between dietary calcium intake or supplementation and the occurrence of heart attack, stroke risk or death from cardiovascular disease.

What did the research involve?

The researchers used data from 23,980 people, aged 35 to 64 years old at the start of the study, from the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition study.

The participants were all living in Germany and were initially free of any major heart problems. They were followed up for an average of 11 years, in which time incidents of heart attack (myocardial infarction), stroke and death from cardiovascular disease were recorded.

The researchers recorded total dietary calcium intake for a sub-sample of 104 participants as part of a broader assessment of diet. This self-administered assessment used a validated 148-item food frequency questionnaire before the participants enrolled on the study.

In subsequent follow-up surveys, all participants were asked if they had regularly taken vitamin or mineral supplements in the past four weeks. “Regularly” was defined as use for at least one week or non-daily use of at least five doses on a regular basis. Self-reported supplements were recorded but data on dosage was not collected.

Researchers then defined four groups:

users of calcium supplements with other vitamins or minerals

users of calcium supplements alone

users of other vitamin or mineral supplements

non-users of any supplement

The researchers also divided up the people in the study into four quarters, based on total dietary calcium intake.

Incidents of heart attack, stroke and death from cardiovascular disease were reported by next of kin in follow-up interviews and verified by tracking medical records or official death certificates.

The statistical analysis adjusted for several additional factors that may influence the relationship between dietary calcium intake and heart health. These included gender, age, level of education, physical activity levels, smoking status, alcohol intake and total protein intake. Analysis of the effects of calcium supplementation also adjusted for total dietary calcium intake, high fat levels and use of non-steroidal anti-inflammatory drugs (NSAIDs).

What were the basic results?

Of the 23,980 participants enrolled in the study:

15,959 used no supplements

851 used calcium supplements only

7,170 used other supplements

Over the 11-year period there were 354 heart attacks, 260 strokes and 267 deaths from cardiovascular disease.

The only statistically significant association between dietary calcium levels and heart attack risk showed that higher levels of calcium were associated with a lower risk. Compared with those in the first quarter (lowest) of total dietary calcium intake, the third quarter (second-highest quarter of intake) had a 31% lower relative risk of suffering a heart attack (hazard ratio 0.69, 95% confidence interval 0.50 to 0.94). A similar comparison looking only at intake of dairy calcium showed that the third quarter had a 32% lower relative risk (hazard ratio 0.68, 95% confidence interval 1.17 to 2.96).

Overall, the researchers found no associations between calcium intake or supplementation and the risk of stroke or of death due to cardiovascular disease.

Calcium supplement use was found to be associated with an 86% increase in the risk of heart attack compared with non-users of any supplements (hazard ratio 1.86, 95% confidence interval 1.17 to 2.96), which was more pronounced in those taking only calcium supplements (hazard ratio 2.39, 95% confidence interval 1.12 to 5.12). This means that those who took calcium supplements as their only supplement were 2.39 times more likely to have a heart attack than those not taking any supplement over the 11-year follow-up period.

How did the researchers interpret the results?

The researchers remarked that heart attack risk “might be substantially increased by taking calcium supplements” and concluded that the pills “should be taken with caution” because they appeared to raise the annual risk of heart attack.

Conclusion

This large prospective cohort study following more than 23,000 German adults over 11 years showed that those regularly taking only calcium supplements were at a higher risk of heart attack compared with those not taking supplements.

This study has many strengths, including its large size and its prospective nature over a relatively long period of 11 years.

However, while this study does highlight an association, it doesn’t prove that calcium supplementation causes more heart attacks. There are potentially other factors, some measured in the study and some not, which could influence the link between calcium supplementation and incidence of heart attack.

For example, compared with non-users, the study reported that those taking calcium supplements only were more likely to:

be older

be less well-educated

have smoked for longer

These are all factors that could contribute to poorer heart health. However, the people taking calcium supplements only were also more likely to be:

women

physically active

a healthy weight

These are all factors that promote good heart health. This contradiction highlights that there can be many fundamental differences between people who use calcium supplements and those who don’t. Not all of these differences will have been taken into account in the statistical analyses of the results and so some uncertainty remains as to how strong the association is.

However, there have been several randomised controlled trials of calcium supplements and their effect on heart disease, which have shown similar results to the current study. Taken together, these studies strengthen the link between calcium supplements and heart disease. But supplements are often taken for good reasons and so it is important for health professionals to help to determine whether the potential risks of taking calcium supplements outweigh the benefits for each individual.

If you have been prescribed calcium supplements, don’t be alarmed by the headlines. Don’t stop taking your medication, but speak to your doctor if you have particular concerns.